What is the formula for calculating energy transfer?

• A. Ingested ÷ Biomass × 100
• B. Biomass × Ingested
• C. Biomass ÷ Ingested × 100
• D. Ingested − Biomass

Answer: (C)

The main idea here is energy transfer efficiency between trophic levels, which tells us what fraction of the energy from the level below actually becomes biomass at the next level. To get that percentage, you compare how much energy is stored as biomass at the higher level to how much energy was available at the lower level to start with. You divide the higher-level biomass by the ingested energy from the level below and then multiply by 100 to express it as a percent. This gives the portion of energy that moves up as new biomass.

Why the other forms aren’t correct: taking the inverse, ingested divided by biomass, would give the opposite fraction and isn’t the transfer efficiency. Multiplying biomass by ingested mixes two quantities that shouldn’t be combined that way and doesn’t yield a percentage of energy transfer. Subtracting ingested from biomass shows a difference in amounts but not the proportion transferred, so it doesn’t measure transfer efficiency either.